Magnetic pulser circuit for material tester

ABSTRACT

A high voltage magnetic pulser circuit is described which is used, for example, in an ultrasonic nondestructive material testing system. The circuit includes a saturable core transformer which is driven into saturation by the output of a synchronized pulse multivibrator at repetitious intervals. Upon saturation the output voltage on the secondary winding of the transformer has reached a relatively high voltage. Thereafter, the sharp down slope of the voltage creates the leading edge of the pulse and induces a resonant circuit coupled thereto into oscillation. Because of the high level of the signal induced into the resonant circuit from the transformer, the inductor therein also saturates and the trailing edge of the pulse is sharply established. After saturation the resonant circuit is caused to quickly discharge, and thus provide a low impedance to an attached L.C. tuned circuit or the like. The result is a high voltage pulse at a desired frequency.

7 United State:

I feet Couture MAGNETIC PULSER CIRCUIT FOR MATERIAL TESTER lnventor:John W. Couture, Danbury, Conn.

Assignee: Automation Industries, Inc., Los Angeles,

Calif.

May 13, 1971 Related U.S. Application Data Continuation of Ser. No.794,053, Jan. 27, 1962, abandoned.

Filed:

Appl. No.:

US. Cl. ..73/67.8 R, 328/67 Int. Cl. ..G0ln 29/00 Field of Search....73/67.8, 67.9; 307/268;

References Cited UNITED STATES PATENTS Wood ..73/67.9

Johannessen ..328/67 Farrell ..328/67 5151 3,673,859 July 4, 1972 OTHERPUBLlCATlONS G.E. Transistor Manual, 1964, pp. 200- 203 PrimaryExaminerRichard C. Queisser Assistant Examiner-Arthur E. KorkoszAttorney--Dan R. Sadler [57] ABSTRACT A high voltage magnetic pulsercircuit is described which is used, for example, in an ultrasonicnondestructive material testing system. The circuit includes a saturablecore transformer which is driven into saturation by the output of asynchronized pulse multivibrator at repetitious intervals. Uponsaturation the output voltage on the secondary winding of thetransformer has reached a relatively high voltage. Thereafter, the sharpdown slope of the voltage creates the leading edge of the pulse andinduces a resonant circuit coupled thereto into oscillation. Because ofthe high level of the signal induced into the resonant circuit from thetransformer, the inductor therein also saturates and the trailing edgeof the pulse is sharply established. After saturation the resonantcircuit is caused to quickly discharge, and thus provide a low impedanceto an attached L.C. tuned circuit or the like. The result is a highvoltage pulse at a desired frequency.

18 Claims, 3 Drawing Figures l jaa AAAAA PATENTEDJUH I972 SHEET 2 OF 2 fWe M y 50 5% VJ WM Oh I 4 l W fi All NW fi W bib) W N\ m I MAGNETICPULSER CIRCUIT FOR MATERIAL TESTER CROSS REFERENCE TO RELATEDAPPLICATION This is a Continuation of co-pending application. Ser. No.794,053 filed Jan. 27, 1969, now abandoned for Magnetic Pulser Circuitfor Material Tester on behalf of John W. Couture.

BACKGROUND OF THE INVENTION A. Field of the Invention This inventionrelates to an electrical pulse generator, and more particularly to anovel and improved pulser useful in generating magnetic pulses for anultrasonic nondestructive material tester or the like.

B. Description of the Prior Art In the prior art there is providedelectrical nondestructive test equipment which generates ultrasonicvibrations by use of a crystal transducer. The vibrations from thetransducer are then sent in the form of an acoustical pulse beamed intothe workpiece being tested. The beam travels unimpeded through theworkpiece and reflects back from the surfaces thereof. Any flaw, defector any other discontinuity in the workpiece also causes reflections ofthe acoustical beam back to the instrument which indicates the locationand size of the discontinuity on a display, such as an oscilloscope.

The echo return energy is amplified and displayed on the oscilloscope asvertical spikes. The screen on the oscilloscope shows spikes of theinitial pulse, the defect, and the back and front surface reflections ofthe workpiece. Spacing of the spikes on the scope is in proportion tothe distance the beam travels and the material tested, thus, locatingthe position of any flaw by irregular spaced spikes.

In order to generate proper electrical pulses to be transmitted to thesearch unit and to cause the transducer therein to vibrate, a pulsegenerator is necessary to generate a high voltage, high frequency pulse.I-Ieretofore, prior art devices included the use of a thyratron tube inorder to generate these pulses. Such thyratron pulsers are undesirablebecause of their slow speed, slow warm up time, their unreliability andtheir expensive cost. Further, these earlier ultrasonic pulsers had aslow pulse repetition frequency because of their use of electronicdischarge tubes, such as the thyratron. They were normally large in sizeand were dependent upon the active element parameters for their risetimes. Because of the above stated limitations, the prior art pulsegenerators are considered quite expensive for real high speed materialtesting units such as those now in present use.

SUMMARY OF THE INVENTION Briefly described the present inventionincludes means for forming a synchronized pulse such as an oscillatorand shape the pulse to have a fall time at a predetermined interval. Asaturable core step-up transformer is provided which includes an inputwinding coupled to receive the pulses provided by the source at therepetitiously spaced intervals. The transfonner is saturated by thepulse from the source at these predetermined times. A resonant circuitis provided and coupled to the output winding of the transformer and isadapted to oscillate for a predetermined interval and saturatethereafter. Means are provided for discharging the resonant circuit uponsaturation thereof and whereby the saturation of the transformer and theoscillation and discharging of the resonant circuit establish the highvoltage pulse.

One feature of this invention is that a circuit is provided toaccommodate high voltage levels without the use of expensive electrondischarge tubes, such as the thyratron, or expensive high voltagetransistors. The resolution is improved both by the shorter minimumpulse length and by cessation of low level ringing at a sooner timeinterval for both minimum and maximum pulse lengths. By proper controlof the parameters of the circuit, both rise and fall times are easilycontrolled which provides for more efficient excitation of the crystalin the search unit. This contrasts with the exponential fall nowprovided on the prior art pulsers.

A further feature of this invention is the circuit provides a low powerconsumption and operates at a lower temperature.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF A PREFERRED EMBODIMENTTurning now to FIG. 1 there is shown a nondestructive testing instrument10 which produces a series of intermittently occurring high voltage,high frequency pulses as will be explained in more detail in connectionwith FIG. 3. Pulse generator 11 is coupled to a transmitter 12 whichtransmits these high frequency pulses into the search unit 14. Thetransmitter 12 may be coupled to the search unit 14 by a coaxial cable16. The pulses emitted by the transmitter 12 excite the transducer 16within the search unit 14 whereby corresponding pulses of electrosonicenergy are transmitted therefrom.

Echoes from the pulses are received by the search unit 14 whereby acorresponding electrical signal is produced therefrom. Thiscorresponding electrical signal is returned through the cable 16 toreceiver 18. The receiver 18 is coupled to a vertical deflectiongenerator 19, which in turn is coupled to an oscilloscope 20. The pulsegenerator 1 l is also coupled to a horizontal sweep generator 22, whichin turn is also coupled to the oscilloscope 20. The results of theoutput of the vertical deflection generator are reflected by thereceiver 18, and the results obtained in conjunction with the signalfrom the horizontal sweep generator 22 are displayed as the display 24as exhibited on the face of the oscilloscope 20. The display 24 on theoscilloscope 20 reflects the return energy in the form of spikesindicative of the initial pulse, the front surface reflections, thedefects, and the back surface reflections from the material beingtested. Spacing of the spikes is in proportion to the distance of thereflections from the material under test. Any random spike which appearsbetween the initial spacing is indicative of flaws, defects or otherdiscontinuities in the workpiece. Thus, the presence and location ofthese flaws are identifiable by the random spikes between the initialreturn spikes.

With reference now to FIG. 3 there is shown an input terminal 52 whichis coupled to a source of repetitiously spaced electrical pulses, asshown in Graph A of FIG. 2. The terminal 52 is coupled to amultivibrator 30 which is comprised of the transistors Q1 and Q2 showntherein. The multivibrator 30 supplies pulses of predetermined pulsewidths, as shown in Graph B of FIG. 2. The pulse width can be varied bythe variable resistor 53. The signal from the multivibrator 30 is thenapplied to a driver circuit 32 which drives the pulses to a higher levelbefore applying them to amplifier 34. The amplifier 34 amplifies thepulses from the driver 32 to approximately 300 volts and applies them toa transformer 60.

The transistor Q5 of the amplifier 34 has its collector coupled throughan inductor 62 to one leg of the secondary winding 64 of the transformer60. A diode 68 is coupled between the collector of the transistor Q5 ofthe amplifier 34 and the other leg of the secondary winding 64 oftransformer 60. For this embodiment the terminal 70 may have 300 voltsapplied thereto. The inductor 62 limits the current the amplifier 34delivers to the transformer 60 when in magnetic saturation. The diode 68limits the voltage overshoot on the turn off of the amplifier 34.

Q5 which forms the amplifier 34 drives the transformer 60 from the 300volts on the terminal 71 to a high voltage (for example 1,100 volts) onthe secondary winding 72 thereof. Because of the high voltage thetransformer 60 saturates shortly thereafter. The saturation generatesthe leading edge of the output pulse. With reference to Graph C FIG. 2,there is shown the wave form appearing on the secondary winding 72 whichexhibits a rapid collapse of voltage at the time of saturation of thetransfonner 60.

One end of the secondary winding 72 of transformer 60 is coupled to aground reference, and the other end is coupled to the cathode of a diode74 and to one electrode of a capacitor 76. The anode of diode 74 iscoupled through a resistor 78 to the ground reference. The otherelectrode of capacitor 76 is coupled to a plurality of series coupledcapacitors 80, 82, 84, 86 and 88 to the ground reference. A plurality ofcorresponding series coupled diodes 90, 92, 94 and 96 are coupledbetween the capacitor 76 and a l2 volt source through a resistor 98.Each diode 90, 92, 94, and 96 is coupled in parallel with acorresponding capacitor 80, 82, 84, and 86, respectively. The diode 74and resistor 78 act as a selective damping network for negativesecondary voltages provided on the secondary winding 72 of transformer60. The value of resistor 78 is detemiined by the damping overshoot ofthe signal, for example 33 Ohms. The capacitor 76 stores the secondaryvoltage from transformer 60 prior to saturation of the transformer. Thediodes 90, 92, 94 and 96 prevent positive signals from passing thepositive portion of the wave form shown in Graph C in FIG. 2 with theamplified results as set forth in the wave form shown in Graph D in FIG.2. The capacitors 80, 82, 84 and 86 balance the drop on the diodes 90,92, 94 and 96 to regulate the conductance thereof.

A saturable core inductor 103 has one end coupled to a junction 106between the capacitor 76 and the series coupled diodes 90, 92, 94 and96. The other end of inductor 103 is coupled to a ground reference.Inductor 103 aids in shaping the exciting pulse. When saturatinginductor 103 generates the trailing edge of the exciting pulse. Aftersaturating transformer 60 discharges through diodes 90, 92, 94 and 96which are now a low impedance path to ground.

The saturation action of the transformer 60 generates the front edge ofthe exciting pulse as exhibited by the sharp fall of the wave form shownin Graph C, which in turn is the front edge of the exciting pulse shownin Graph D. The junction 106 which appears between the diodes 76 and thecapacitors 80, 82, 84, 86 and 88 and the diodes 90, 92, 94 and 96 arecoupled to a pair of back-to-back diodes 108 and 110 and also coupled toa switch 112. The other end of the back-to-back coupled diodes 108 and110 is coupled to an inductor 114 which has a plurality of tappedoutputs which is operable with a switch 116. The diodes 108 and 110reject noise generated by the turn off of transformer 60 and diode 74and also reduces noise generated by inductor 103.

The switch 112 is operable with a plurality of terminals 118, 120, 122and 124 and is adapted to couple the junction 106 to a selected one ofthese terminals. The switch arm 112 is mechanically coupled to theswitch arm of the switch 116, which in turn is mechanically coupled tothe switch arm of a switch 128.

The saturable core inductor 103 has one end coupled to the switchterminal 124 and includes a tap 132 coupled to the terminals 118, 120and 122. The other end of the saturable core inductor 103 is coupled tothe ground reference.

The switch arm of the switch 116 is adapted to be positioned on one ofthe terminals 134, 136, 138 and 140 which are coupled to respectiveoutput taps of the transformer 114. The switch arm of the switch 116 iselectrically and mechanically coupled to the switch arm of the switch128. The switch arm of the switch 128 is adapted to be positioned to aselected terminal 142, 144 or 146. Terminal 142 is coupled through acapacitor 150 to the ground reference. Terminal 144 is coupled through acapacitor 152 to a ground reference. Terminal 146 is coupled through acapacitor 154 to the ground reference. Inductor 103 and a selected oneof the capacitors I50, I52 and 154 form a resonant circuit and willresonate during the saturation period of the transformer 60. Theselection is responsible for generating the proper frequency on theoutput pulse as set forth in Graph E of FIG. 2. After saturation oftransfonner 60 the capacitor 76 transfers its stored voltage to inductor103 and aids in the saturating action of both inductor 103 andtransformer 60.

The capacitor 88 and resistor 98 generate a negative current source toaid in resetting inductor 103 after saturation. The capacitor 88 andresistor 98 also maintain a forward bias on diodes 90, 92, 94 and 96thereby eliminating turn off noise generated by transformer 60 and diode74. The current source provided by capacity 88 and resistor 98 isovercome when capacitor 76 is transferring its stored voltage to theinductor 103.

A resistor has one leg coupled to the junction between the switch armsof switches 116 and 128 and to the anode of a diode 162. The cathode ofthe diode 162 is coupled to the other leg of the resistor 160 andthrough a resistor 164 to one end of a potentiometer 166, the end ofwhich is coupled to the ground reference.

A diode bridge comprises the diodes 172, 174, 176 and 178 and the zenerdiode 180 and capacitor 182. The switch arm of switch 128 is coupled tothe junction between diodes 172 and 174. The junction between diodes 172and 178 is coupled through a resistor 184 to the -l2 voltage source andthe junction between diodes 174 and 176 is coupled through a resistor186 to a +12 voltage source. Capacitors 188 and 190 are provided to theresistors 184 and 186 respectively, to provide a constant current sourcethrough the bridge 170. The bridge 170 is provided to remove theundesired noise created by the preceding components. Also causescessation of low level ringing at a sooner time interval for bothminimum and maximum pulse length. The junction between the diodes 176and 178 provides the output circuit to the output terminal 192 whichprovides the output pulse created to the transducer 14 for providing thecorresponding ultrasonic pulse into the workpiece.

The junction between diode 176 and 178 is also coupled through resistor194 and variable resistor 196 to the ground reference. The resistors 196and 166 may be in the form of rheostats which have their wiper armsmechanically ganged together. By moving the wiper arms of the rheostats,the length of the pulse on the output terminal 192 may be variedaccordingly.

In summation it has been shown that the transformer 60 receives pulsesin a synchronized order from the multivibrator 30 through the driver 32and amplifier 34. The pulse is stepped-up on the secondary winding 72,and the transformer 60 thereafter saturates when the voltage reaches apredetermined level. A resonant circuit comprised of the inductors 103and 114 and the capacitor 76 goes into an oscillatory transient. Theinductor 103 cannot, however, withstand this level of oscillation withcapacitor 76 and responds by sustaining only a portion of theoscillation cycle and then saturating. The time relationship between thesaturation of transformer 60, partial oscillation of capacitor 76 withinductor 103, and the subsequent saturation of inductor 103 provides thenecessary pulse width for each output pulser frequency. The inductor 103after saturating then begins to discharge through diodes 90, 92, 94 and96 and through resistor 98. These diodes, now forward biased, provide alow impedance path and assist in a fast fall time on the pulse.

By manipulation of the switches 112, 116 and 128 the resonantfrequencies and charge and discharge times of the components thereof arechanged. Thus the shape of the wave form is changed accordingly. Thesaturation of inductor 103 controls the trailing edge of the pulse incombination with the inductor 1 14 controls the resonant frequency whichin turn controls the pulse width.

After the pulse signal has been formed it is transmitted by transmitter12 into the transducer 14 for use in material testing. The signaltransmitted is now the desired high frequency, high voltage pulse andreadily available at faster intervals.

Having thus described but one preferred embodiment of his invention,what is claimed is: i

l. The combination of a source of timing pulses,

a square wave generator coupled to said source and effective to providea square wave in response to each of said timing pulses,

a saturable core transformer,

a primary in said transformer coupled to said square wave generator forreceiving the square waves therefrom, the core of said transformer beingeffective to saturate when the square wave reaches a predeterminedlevel,

a secondary in said transformer,

a saturable core inductor coupled to said secondary of said transformer,the core of said inductor being adapted to saturate a predetermined timeafter the core of said transformer saturates,

a resonant circuit coupled to said inductor and to said secondary, saidcircuit being effective to resonate for a predetermined time when thesignal induced in said secondary attains a predetermined level, and

an ultrasonic transducer coupled to said resonant circuit and responsiveto the signal therefrom for transmitting ultrasonic energy.

2. The combination of claim 1 including means for varying the resonantfrequency of said circuit.

3. The combination of claim 1 including a plurality of discharge diodescoupled to said resonant circuit and effective to conduct when saidinductor saturates. I

4. The combination of claim 3 including a receiver coupled to saidtransducer.

5. A nondestructive test system for inspecting workpieces including asource of timing pulses,

a saturable core transformer having an input winding and an outputwinding, said input winding being coupled to said source for receivingsaid timing pulses for establishing the leading edge of a higher voltagepulse,

a resonant circuit coupled to the output winding of said transformer,said circuit being adapted to resonate for a predetermined time when thesignal induced into the output winding of said transformer attains apredetermined level for establishing the traling edge of the highervoltage pulse,

a search unit for being acoustically coupled to the workpiece, saidsearch unit being coupled to the resonant circuit for transmittingcorresponding ultrasonic vibrations into the workpiece and for receivingechoes of the ultrasonic energy and for providing correspondingelectrical signals,

receiving means responsive to said transducer for receiving thecorresponding electrical signals, and

display means coupled to said receiving means for providing a displayindicative of the electrical signals from said receiving means.

6. The nondestructive test system as defined in claim 5 including meansfor discharging said resonant circuit after said resonant circuit hasresonated for a predetermined time for establishing the trailing edge ofthe higher voltage pulse.

7. A nondestructive test system for inspecting workpieces including asource of timing pulses,

a saturable core transformer having an input winding and output winding,said input winding being coupled to said source and responsive to saidtiming pulses for establishing the leading edge of a higher voltagepulse,

a resonant circuit coupled to the output winding of said transformer,said circuit being adapted to resonate in response to the signal inducedinto the output winding of said transformer,

an inductor coupled to the output winding of said transformer, saidinductor being effective to saturate after a predetermined time forestablishing the trailing edge of the higher voltage pulse,

a search unit for being acoustically coupled to the workpiece, saidsearch unit being coupled to the resonant circuit and responsive to saidhigher voltage pulse for transmitting ultrasonic energy into theworkpiece,

said search unit being effective to receive echoes of the ultrasonicenergy returning from the workpiece for providing correspondingelectrical signals,

receiving means coupled to said search unit for receiving thecorresponding electrical signals, and

display means coupled to said receiving means and responsive to saidsignal for providing a display indicative of the electrical energyreceived by said receiving means.

8. The nondestructive testing system as defined in claim 5 includingmeans for varying the resonance frequency of said resonant circuit.

9. A nondestructive test system for inspecting a workpiece including asaturable core transformer having a primary and a secondary, saidprimary being adapted to receive a series of timing pulses, saidsecondary being adapted to provide a high level output signal inresponse to each timing pulse, the core of said transformer beingadapted to saturate each time a timing pulse reaches a predeterminedlevel,

a resonant circuit coupled to said secondary and effective to resonatefor a predetermined time when said high level output signal in saidsecondary attains a predetermined level,

an inductor coupled to said secondary and effective to saturate after apredetermined time,

diode means coupled to the secondary of said transformer and effectiveto conduct when said inductor saturates,

a search unit for being acoustically coupled to the workpiece, saidsearch unit being coupled to said diode means for transmittingultrasonic energy into the workpiece corresponding to the resonance insaid circuit and for receiving echo returns of ultrasonic energy and forproviding an electrical signal corresponding thereto, and

receiving means coupled to said search unit for receiving thecorresponding electrical energy.

10. A nondestructive test system as defined in claim 9 including asource of timing pulses,

a monostable multivibrator coupled to said source and adapted to receivesaid timing pulses and to provide output pulses of predetermined pulsewidths, and

an amplifier coupled to said monostable multivibrator and to saidprimary, said amplifier being adapted to amplify the output pulses ofsaid monostable multivibrator and apply said pulses to the primary insaid saturable core transformer.

11. A nondestructive test system as defined in claim 9 including meansfor varying the resonance frequency of said resonant circuit.

12. A nondestructive test system as defined in claim 9 including displaymeans coupled to said receiving means for providing a display indicativeof the electrical signal received by said receiving means.

13. A nondestructive test system as defined in claim 9 including meansfor varying the resonance frequency of said resonant circuit, and

display means coupled to said receiving means for providing a displayindicative of the electrical signal received by said receiving means.

14. A nondestructive test system as defined in claim 9 including asource of timing pulses,

a monostable multivibrator coupled to said source to receive said timingpulses from said source and to provide output pulses of predeterminedpulse width,

an amplifier coupled to said source and effective to amplify the outputpulses of said monostable multivibrator, said amplifier being coupled tosaid primary for supplying said amplified signal to said saturable coretransformer, and

means to vary the resonance frequency of said resonant circuit.

15. The nondestructive test system as defined in claim 14ineludingdisplay means coupled to said receiving means for providing a displayindicative of the electrical signal received by said receiving means.

16. A nondestructive test system for inspecting a workpiece including asearch unit for being acoustically coupled to the workpiece andtransmitting ultrasonic energy into the workpiece in response to adriving signal,

first inductive means having a saturable core,

a source of timing signals coupled to said first inductor means forsupplying the timing signals thereto whereby a second signal is producedin the winding means, said timing signal being large enough to saturatesaid core,

second inductive means having a saturable core, said second inductivemeans being coupled to the first inductive means and responsive to thesecond signal whereby a driving signal is produced in the secondinductive means,

said second signal being large enough to saturate the second core, and

means coupling the second inductive means to the search unit forsupplying said driving signal thereto.

17. A nondestructive test system for inspecting a workpiece including asearch unit for being acoustically coupled to the workpiece andtransmitting ultrasonic energy into the workpiece in response to adriving signal,

a transformer having a saturable core together with an input winding andan output winding,

a source of timing pulses coupled to said input winding for supplyingtiming pulses thereto whereby a higher voltage pulse is produced in theoutput winding, said timing pulses being large enough to saturate thecore of said transformer, and

a driving circuit coupled to the output winding of said transformer andresponsive to the higher voltage pulses to provide a series of drivingsignals, said driving circuit being coupled to the search unit forsupplying said driving signals thereto.

18. A nondestructive test system for inspecting a workpiece including asearch unit for being acoustically coupled to the work piece andtransmitting ultrasonic energy into the work piece in response to adriving signal,

a transformer having a saturable core together with an input winding andan output winding,

a source of timing pulses coupled to said input winding for supplying atinting pulse thereto whereby a higher voltage pulse is produced in theoutput winding, said timing pulses being large enough to saturate thecore of said transformer,

second inductive means with a saturable core and winding means, saidwinding means being coupled to the output winding of said transformerand responsive to the higher voltage pulses therefrom to thereby providea driving signal in the winding means, said higher voltage pulse beinglarge enough to saturate the second core, and

a driving circuit coupling the second inductive means to the search unitfor supplying said driving signal thereto.

1. The combination of a source of timing pulses, a square wave generatorcoupled to said source and effective to provide a square wave inresponse to each of said timing pulses, a saturable core transformer, aprimary in said transformer coupled to said square wave generator forreceiving the square waves therefrom, the core of said transformer beingeffective to saturate when the square wave reaches a predeterminedlevel, a secondary in said transformer, a saturable core inductorcoupled to said secondary of said transformer, the core of said inductorbeing adapted to saturate a predetermined time after the core of saidtransformer saturates, a resonant circuit coupled to said inductor andto said secondary, said circuit being effective to resonate for apredetermined time when the signal induced in said secondary attains apredetermined level, and an ultrasonic transducer coupled to saidresonant circuit and responsive to the signal therefrom for transmittingultrasonic energy.
 2. The combination of claim 1 including means forvarying the resonant frequency of said circuit.
 3. The combination ofclaim 1 including a plurality of discharge diodes coupled to saidresonant circuit and effective to conduct when said inductor saturates.4. The combination of claim 3 including a receiver coupled to saidtransducer.
 5. A nondestructive test system for inspecting workpiecesincluding a source of timing pulses, a saturable core transformer havingan input winding and an output winding, said input winding being coupledto said source for receiving said timing pulses for establishing theleading edge of a higher voltage Pulse, a resonant circuit coupled tothe output winding of said transformer, said circuit being adapted toresonate for a predetermined time when the signal induced into theoutput winding of said transformer attains a predetermined level forestablishing the traling edge of the higher voltage pulse, a search unitfor being acoustically coupled to the workpiece, said search unit beingcoupled to the resonant circuit for transmitting correspondingultrasonic vibrations into the workpiece and for receiving echoes of theultrasonic energy and for providing corresponding electrical signals,receiving means responsive to said transducer for receiving thecorresponding electrical signals, and display means coupled to saidreceiving means for providing a display indicative of the electricalsignals from said receiving means.
 6. The nondestructive test system asdefined in claim 5 including means for discharging said resonant circuitafter said resonant circuit has resonated for a predetermined time forestablishing the trailing edge of the higher voltage pulse.
 7. Anondestructive test system for inspecting workpieces including a sourceof timing pulses, a saturable core transformer having an input windingand output winding, said input winding being coupled to said source andresponsive to said timing pulses for establishing the leading edge of ahigher voltage pulse, a resonant circuit coupled to the output windingof said transformer, said circuit being adapted to resonate in responseto the signal induced into the output winding of said transformer, aninductor coupled to the output winding of said transformer, saidinductor being effective to saturate after a predetermined time forestablishing the trailing edge of the higher voltage pulse, a searchunit for being acoustically coupled to the workpiece, said search unitbeing coupled to the resonant circuit and responsive to said highervoltage pulse for transmitting ultrasonic energy into the workpiece,said search unit being effective to receive echoes of the ultrasonicenergy returning from the workpiece for providing correspondingelectrical signals, receiving means coupled to said search unit forreceiving the corresponding electrical signals, and display meanscoupled to said receiving means and responsive to said signal forproviding a display indicative of the electrical energy received by saidreceiving means.
 8. The nondestructive testing system as defined inclaim 5 including means for varying the resonance frequency of saidresonant circuit.
 9. A nondestructive test system for inspecting aworkpiece including a saturable core transformer having a primary and asecondary, said primary being adapted to receive a series of timingpulses, said secondary being adapted to provide a high level outputsignal in response to each timing pulse, the core of said transformerbeing adapted to saturate each time a timing pulse reaches apredetermined level, a resonant circuit coupled to said secondary andeffective to resonate for a predetermined time when said high leveloutput signal in said secondary attains a predetermined level, aninductor coupled to said secondary and effective to saturate after apredetermined time, diode means coupled to the secondary of saidtransformer and effective to conduct when said inductor saturates, asearch unit for being acoustically coupled to the workpiece, said searchunit being coupled to said diode means for transmitting ultrasonicenergy into the workpiece corresponding to the resonance in said circuitand for receiving echo returns of ultrasonic energy and for providing anelectrical signal corresponding thereto, and receiving means coupled tosaid search unit for receiving the corresponding electrical energy. 10.A nondestructive test system as defined in claim 9 including a source oftiming pulses, a monostable multivibrator coupled to said source andadapted to Receive said timing pulses and to provide output pulses ofpredetermined pulse widths, and an amplifier coupled to said monostablemultivibrator and to said primary, said amplifier being adapted toamplify the output pulses of said monostable multivibrator and applysaid pulses to the primary in said saturable core transformer.
 11. Anondestructive test system as defined in claim 9 including means forvarying the resonance frequency of said resonant circuit.
 12. Anondestructive test system as defined in claim 9 including display meanscoupled to said receiving means for providing a display indicative ofthe electrical signal received by said receiving means.
 13. Anondestructive test system as defined in claim 9 including means forvarying the resonance frequency of said resonant circuit, and displaymeans coupled to said receiving means for providing a display indicativeof the electrical signal received by said receiving means.
 14. Anondestructive test system as defined in claim 9 including a source oftiming pulses, a monostable multivibrator coupled to said source toreceive said timing pulses from said source and to provide output pulsesof predetermined pulse width, an amplifier coupled to said source andeffective to amplify the output pulses of said monostable multivibrator,said amplifier being coupled to said primary for supplying saidamplified signal to said saturable core transformer, and means to varythe resonance frequency of said resonant circuit.
 15. The nondestructivetest system as defined in claim 14 including display means coupled tosaid receiving means for providing a display indicative of theelectrical signal received by said receiving means.
 16. A nondestructivetest system for inspecting a workpiece including a search unit for beingacoustically coupled to the workpiece and transmitting ultrasonic energyinto the workpiece in response to a driving signal, first inductivemeans having a saturable core, a source of timing signals coupled tosaid first inductor means for supplying the timing signals theretowhereby a second signal is produced in the winding means, said timingsignal being large enough to saturate said core, second inductive meanshaving a saturable core, said second inductive means being coupled tothe first inductive means and responsive to the second signal whereby adriving signal is produced in the second inductive means, said secondsignal being large enough to saturate the second core, and meanscoupling the second inductive means to the search unit for supplyingsaid driving signal thereto.
 17. A nondestructive test system forinspecting a workpiece including a search unit for being acousticallycoupled to the workpiece and transmitting ultrasonic energy into theworkpiece in response to a driving signal, a transformer having asaturable core together with an input winding and an output winding, asource of timing pulses coupled to said input winding for supplyingtiming pulses thereto whereby a higher voltage pulse is produced in theoutput winding, said timing pulses being large enough to saturate thecore of said transformer, and a driving circuit coupled to the outputwinding of said transformer and responsive to the higher voltage pulsesto provide a series of driving signals, said driving circuit beingcoupled to the search unit for supplying said driving signals thereto.18. A nondestructive test system for inspecting a workpiece including asearch unit for being acoustically coupled to the workpiece andtransmitting ultrasonic energy into the work piece in response to adriving signal, a transformer having a saturable core together with aninput winding and an output winding, a source of timing pulses coupledto said input winding for supplying a timing pulse thereto whereby ahigher voltage pulse is produced in the output winding, said timingpulses being large enough to saturate the core of said transformer,second inductive means with a saturable core and winding means, saidwinding means being coupled to the output winding of said transformerand responsive to the higher voltage pulses therefrom to thereby providea driving signal in the winding means, said higher voltage pulse beinglarge enough to saturate the second core, and a driving circuit couplingthe second inductive means to the search unit for supplying said drivingsignal thereto.